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End of Day Email: Febuary 21st 2013
Well, I seem to see a correlation between starting sending these emails and the market sell off. I think it is spurious. I wanted to take most of this email talking about SRPT. I listened to the FDA/DMD talk (https://cc.readytalk.com/cc/playback/Playback.do) and my impression is that there is nothing new in it. It is useful in that it highlights some signposts that we need to follow. There are a couple of points I want to highlight.
1. Just so we are all on the same page here is the wording from the FDA about accelerated approval.
"FDA may grant marketing approval for a new drug product on the basis of adequate and well-controlled clinical trials establishing that the drug product has an effect on a surrogate endpoint that is reasonably likely, based on epidemiologic, therapeutic, pathophysiologic, or other evidence, to predict clinical benefit or on the basis of an effect on a clinical endpoint other than survival or irreversible morbidity."
2. The first problem that might trip up SRPT is the adequate and well-controlled portion. I don't think this is the major hurdle but certainly is one that people will talk about. The FDA can use historical controls if the progression of the disease is well established. SO I do not think the single arm nature is a major problem. The small number might be in terms of making it difficult to judge the degree and robustness of effect.
3. The larger hurdle, I think, is the relationship between the surrogate endpoint and clinical benefit. The FDA wants to see that changes in the surrogate endpoint is correlated with changes in clinical benefit. SRPT is arguing for dystrophin levels as a surrogate for clinical benefits but results are mixed (http://investorrelations.sareptatherapeutics.com/phoenix.zhtml?c=64231&p=irol-newsArticle&id=1741044). For instance, the 50 mg/kg group had 41.7% increase in dystrophin levels and increased walk by 87.4 meters. In contrast, the 30mg/kg group had 52% increase in dystrophin levels but only an increase of 28.8 meters. So increase in dystrophin leads to less increase in walk and increase in dose leads to less dystrophin but greater change in walk. Keep in mind that I am not saying there is not a relationship but the FDA seemed clear that there needs to be reasonable evidence that surrogate is correlated with clinical benefit. In my mind this is the biggest hurdle SRPT will have to clear.
5. So the take home point that I got from the FDA briefing was mainly that it was informing about the process and there was really nothing new. I think if SRPT can persuasively argue that dystrophin levels correlate with 6MW improvements, then chances increase a lot for AA. Current data are mixed bag and seem to make it difficult to make that case. Keep an eye for new data and any sort of consensus developing around this correlation.
I am also doing something new with this email. I made a short (2 minutes at most) survey about SRPT and chances for accelerate approval. Please take the time to fill it out and then I will organize the results and send them out tomorrow after the market closes. This way we can get a sense of what the consensus on these issues really is instead of guessing. So please take a couple minutes so we can get a nice large number of observations. Thanks.